Master- and PhD-Theses

Master- and PhD-Theses

The USM-MPE extragalactic research group is a joint effort of the University Observatory of Munich (USM) and the Max-Planck Institute for Extraterrestrial Physics. The group is located both at the USM (see `Extragalactic Astronomy') and at MPE. Senior group members are Prof. Ralf Bender, Dr. Maximilian Fabricius, Prof. Ortwin Gerhard, Dr. Ulrich Hopp, P.D. Dr. Roberto P. Saglia, Dr. Ariel G. Sánchez, Dr. Stella Seitz and Dr. Jens Thomas.

The research of the group focuses on dark energy and dark matter in the Universe, on the properties of local and distant galaxies, and on extrasolar planets. The aims of our current science projects are:

to constrain the nature of dark matter by analysing cluster and galaxy dark matter halo profiles with strong and weak lensing in combination with dynamical and photometric information for nearby galaxies

to derive constraints on the nature of dark energy, by studying the large-scale structure of the Universe by means of weak lensing and clustering measurements

to understand the structure and dynamics of local and distant galaxies, their stellar populations, their formation and evolution

to reconstruct the dark matter mass distribution and chemodynamical history of the Milky Way from the current revolutionary survey data, giving us a template for galaxy formation

to quantify the role of black holes and dark matter in galaxies

to search for extrasolar planets and understand their properties (mass, density, atmosphere).

We pursue these science questions with a combination of optical and near-infrared observations, theory, numerical modelling, and data interpretation.

The observational data necessary for our scientific programs come from a large variety of telescopes, primarily ESO telescopes, the Hobby-Eberly Telescope (HET), the 2.7m telescope of the McDonald observatory, the USM 2m Fraunhofer telescope at the Wendelstein observatory in the Bavarian Alps and also space (HST) and survey (e.g. SDSS) telescopes. We also have guaranteed access to ESO telescopes for providing instruments (e.g. OmegaCAM, KMOS, MICADO).

We carry out studies of black holes in local galaxies without active galactic nuclei, measuring their masses through stellar dynamics. Using similar techniques we reconstruct the stellar orbital distributions and dark matter halos of dwarf and giant early-type galaxies or globular clusters. Exploiting the multiplexing capabilities of our KMOS spectrograph, we study galaxy evolution up to redshift 2.5 by observing large samples of star forming and passive galaxies.

Our group also has a significant role in large international surveys. Examples are the completed Baryon Oscillation Spectroscopic Survey (BOSS), the on-going extended BOSS (eBOSS) and Dark Energy Survey (DES), and future surveys such as the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX) and the ESA space mission Euclid. Galaxy clustering and gravitational lensing measurements based on these data sets probe the large-scale structure of the universe with unprecedented precision, providing invaluable information on the nature of dark matter and dark energy, the growth of structure, neutrino masses and inflationary physics. The design, construction, analysis, modelling and interpretation of these data sets are some of the main activities of our group.

The numerical modelling required for our projects is based on state-of-the-art algorithms run on supercomputers. Some of these methods are developed or implemented within our group. Recent examples are Schwarzschild's orbit superposition method used for measuring black hole masses, and the NMAGIC adaptive N-body code for modelling galaxy dynamics.

In addition, the USM-MPE extragalactic research group is designing and building imaging and spectroscopy instruments for 1-10m class telescopes, together with national and international partners. We built, e.g., the FORS1-2 and KMOS instruments for the VLT, the OmegaCAM 1-square-degree imager for VST, all the instruments for the Wendelstein telescopes (WWFI, 3kk, FOCES and VIRUS-W, currently at McDonald Observatory), and the Low Resolution Spectrograph 2 (LRS2) for the 10m HET in Texas (which we share with the Universities of Texas, Penn State University, Standford and Göttingen). We are currently in the design phase of MICADO, a multi-IFU infrared spectrograph that will serve as the first light instrument for the E-ELT, and the near-infrared optical system for the ESA space mission Euclid, planned to be launched in 2020. We also provide software for the giant optical IFU spectrograph VIRUS for HET.

MASTER- AND PHD-THESIS PROJECTS :

Please use our webpages for further information about the research activities of the extragalactic research group at USM and the optical & interpretative astronomy group at MPE. We continuously offer Master projects (please contact us also by email and ask for further projects). Some of the projects listed below are available also as MASTER projects.

PHD THESIS PROJECTS

SUPERVISOR/CONTACT

Project 1 (PhD or Master Project in the Dynamics Group): "Chemodynamical history of the Milky Way"

The Milky Way is the only galaxy whose formation history can be studied star by star. It is currently the focus of extraordinary observational efforts, including both ESA's cornerstone Gaia satellite mission, as well as a multitude of ground-based surveys which are already returning unprecedented data for large numbers of stars. Our group have been at the forefront of clarifying the mass distribution and dynamical structure of the Milky Way's bulge, bar, disk, and dark matter halo from such data.

We have shown that the Milky Way is a typical barred galaxy and that it has a low dark matter fraction in the bulge. The logical next step is to understand the chemodynamical structure in the bulge and disk: where do we find the most metal-rich stars in the Galaxy? Where the stars with high alpha-abundances that formed rapidly in the early phases of the Milky Way? We will develop chemodynamical models to determine the orbit distributions of stars with different abundances, and thereby to constrain the processes by which the Milky Way's bulge, bar, and disk were made.

Our current models show that the data prefer a dark matter density profile with a shallow cusp or core in the central few kpc. The goal of this project it to obtain tighter constraints on the slope of the central dark matter cusp and the flattening of the inner dark halo, and thereby constrain the nature of dark matter. This requires including additional survey data in the modelling, as well as some code development in order to constrain the dark halo parameters during the modelling of the data.

Both project 1 and 2 are suitable for candidates who enjoy working with computational models and applying them to modern large data sets. For more information, see the Webpages of the MPE Dynamics Group, Dynamics Group in particular:* Structure, dynamics, and origin of the Milky Way * Spiral galaxy bulges* Made-to-measure particle models for galaxies

We are performing a systematic 2-dimensional kinematic mapping of the northern nearby dwarf elliptical galaxies with our VIRUS-W instrument at the 2.7m McDonald telescope. Our goal is to measure the stellar kinematics of these objects. This will allow us to constrain the density distribution of the dark matter halos in theseobjects and decide whether a "cusp" (as expected in a Lambda Cold Dark Matter Universe) or a "core" (as suggested by first attempts at these measurements) is present. Moreover, we will investigate the stellar populations by mapping the strength of various absorption line indices: this will allow us to determine the age and metallicity of the galaxies and possibly their gradients. If the galaxies contain ionized gas, we will be able to measure its kinematics too and compare its motions to the stellar ones. The PhD project will involve observation trips at McDonald Observatory, data reduction and analysis and dynamical modeling.

Project 4 (PhD or Master Project in the OPINAS Group): "The internal kinematics of globular clusters"

Even though they are some of the best studied objects in our nearby universe, many questions around the formation mechanisms of globular clusters remain unanswered. We are performing a systematic 2-dimensional kinematic mapping of the northern largest Milky Way globular clusters with our VIRUS-W instrument at the 2.7m McDonald telescope. Our goal is to constrain the internal kinematics of these objects, quantify the amount of global stellar rotation and possibly set constraints on their dark matter content. Moreover, we will investigate the stellar populations by mapping the strength of various absorption line indices: this will allow us to explore the possible gradients in age and metallicity within the globular clusters. The PhD project will involve observation trips at McDonald Observatory, data reduction and analysis and dynamical modeling.

Project 5 (PhD or Master Project in the OPINAS Group): "The formation and orbital structure of disks, classical bulges, pseudo bulges and bars"

The Schwarzschild algorithm solves the collisionless Boltzman equation by superposition of orbits, which represent the space of integrals of motion. By solving for the approriate orbital weights, the method allows to determine the masses of the stars, dark matter halos and central black holes together with the distribution of stellar orbits from observed surface brightness profiles and stellar kinematical maps. Schwarzschild models have been calibrated and work well for elliptical galaxies. Disk galaxies have not been studied in detail yet. Their analysis requires extensions to the currently used implementations of Schwarzschild's method: (1) accurate solutions of the Poisson equation for very flattened disks and for bars are needed; (2) an orbit sampling scheme needs to be developed that ensures inclusion of the many more families of orbits supported by these potentials. The project is aimed to expand the existing Schwarzschild code. In a second step, the student can analyse existing observational data for disk galaxies. The main questions are (1) whether the Mbh-sigma scaling relation is different for disk galaxies with pseudo bulges and with classical bulges and (2) what the orbital structure in disk galaxies tells us about the formation history of their various components.

The masses of the stars, black holes and dark halos of elliptical galaxies thus far have mostly be obtained from dynamical models assuming axial symmetry. Giant ellipticals do not respect this symmetry and previous mass determinations of the stars and of the central black holes may be biased by up to a factor of two. This has important consequences for the slope and intrinsic scatter of global correlations like the famous Mbh-sigma relation. We have finished the development of a triaxial dynamical modelling code using the Schwarzschild orbit superposition technique (see above). Using datasets for massive elliptical galaxies that we already collected in the past, the student can reassess previous measurements of the masses of central black holes, stars and dark matter halos and investigate the implications for widely used global scaling relations.

Project 7 (PhD or Master Project in the OPINAS Group): "The black holes, dark matter halos and IMFs of the most massive galaxies"

At the high-mass end, galaxies have extreme properties: the most massive galaxies host the most massive black holes, they populate the largest dark-matter concentrations in the universe and are believed to be dominated by an extreme population of dwarf stars. MASSIVE is a multi-wavelength survey of the 108 most massive galaxies in the local universe, aiming to investigate their detailed structure and formation histories. As part of the survey, we have collected two-dimensional stellar kinematical maps from subarcsecond scales near the center out to large radii. Dynamical modelling with Schwarzschild orbit superposition models will be used to derive dark matter halo properties and dynamical constraints on the stellar initial-mass-function (IMF). These will be compared with spectroscopic constraints on the stellar populations to study the stellar masses and the assembly histories of these extreme galaxies

Project 8 (PhD or Master Project in the OPINAS Group): "Spectroscopic probes of the Initial Mass Function in local elliptical galaxies"

There is growing evidence that the Initial Mass Function in the central regions of elliptical galaxies might vary systematically with the mass of the systems. We are collecting optical and near infrared two-dimensional spectra of a sample of local elliptical galaxies that should allow us to investigate this issue with a large dataset. The student will derive maps of the IMF-sensitive indices, interprete them with up-to-date stellar population models and compare the results with the constraints coming from dynamics and gravitational lensing.

The student will image SZ, Xray and optically selected clusters with the 30'x30' Wide Field Imager of the 2m telescope on Mt Wendelstein and measure their mass profiles by analyzing the weak lensing effect. The results will be used to constrain the scaling of the mass with the SZ-/Xray/Richness observables. In addition the student is expected to participate in the scientific exploitation of the DES survey regarding cluster and group weak lensing science cases.

We will analyse the strong lensing effect of massive CLASH and Frontier Field galaxy clusters having unique HST imaging data in depth and wavelength coverage. The goal is not only to accurately measure the central 2D projected mass distribution but to in particular constrain the depth and extent of dark matter halos of cluster members and to relate their properties to their stellar light and dynamical measures of their central halo depth. By comparing the cluster galaxy members with field galaxies we'll be able to quantify the amount of tidal halo stripping they undergo when orbiting through dense cluster centers. The student will be a member of the CLASH collaboration.

We will explore the cosmological implications of anisotropic clustering measurements based on galaxy and QSO samples from eBOSS and HETDEX. In particular, we will use measurements of the pattern of baryon acoustic oscillations (BAO) and redshift-space distortions (RSD) to obtain new accurate constraints on the expansion history of the Universe and the growth of density fluctuations. This information offers one of the most powerful routes to constrain the dark energy equation of state parameter, wDE, and its possible evolution with time, or to detect possible deviations from the predictions of general relativity.

Project 12 (PhD or Master Project in the OPINAS Group): "Precision cosmology with the Euclid satellite"

The high-quality data that the Euclid satellite will deliver pose a challenge for our understanding and modeling of LSS observations. As statistical errors become smaller, the control of potential systematic errors becomes essential. The primary uncertainty to compute the likelihood function of Euclid clustering measurements will be to know their associated covariance matrix, C. In most analyses, C is estimated from a set of mock catalogues. However, due to the large volume probed by Euclid this approach might be infeasible. A detailed study of the estimation of C is essential for the success of the mission. We will develop new schemes to minimize the impact of the uncertainties on the covariance matrix as well as theoretical models of C, and use them to compute accurate predictions of the cosmological constraints that can be obtained from Euclid data.